The invention relates to a method for providing an environment map for a vehicle and a corresponding electronic computing device.
It is currently known to capture the surroundings of a vehicle with the aid of sensors such as cameras, lidar, radar or ultrasound. The measurements are often represented in an environment map (sometimes also referred to as a grid), the latter comprising cells to which portions of the surroundings (e.g. 8 cm×8 cm) of the vehicle are assigned. The representation is frequently effectuated by specifying the probability of the portion of the surroundings that is assigned to the respective cell being occupied by an obstacle (obstacle probability). For this reason, this type of environment map is often also referred to as an occupancy grid. Building on the environment map, it is possible to realize many driver assistance systems, such as autonomous cruise control (ACC), highly automated driving or emergency braking assistants, etc. Grid-based approaches for modeling the surroundings (creation of an environment map) are also used with increasing frequency for driver assistance functions, also in the parking and maneuvering context.
During the operation of a vehicle, the environment map is filled in accordance with the measured distance values from a distance-providing sensor system that relate to obstacles in any direction. The measured distance values from a sensor (e.g. an ultrasonic sensor) are converted into an occupancy probability of portions of the surroundings taking into account an obstacle region in the environment map that corresponds in size to the measurement uncertainty and are determined for the corresponding cells. Typically, the obstacle region is greater than a portion of the surroundings that is assigned to a cell, which is why the ascertained obstacle region extends over a plurality of portions and corresponding cells. Usually, the occupancy probabilities are not entered directly as obstacle probabilities into the environment map (even though this is also possible), but instead they are combined by calculation with the previously determined obstacle probabilities. This facilitates a temporal accumulation, and hence averaging, of measurements, which at least partly compensates measurement errors.
Here, the occupancy probabilities ascertained with the aid of the measurement data from a sensor are entered independently of the measurement data from other sensors from one another. This means that the occupancy probabilities that result from the measurement data from a respective sensor are successively entered into the environment map for the purposes of updating the obstacle probabilities.
As a result of the occupancy probabilities that are ascertained with the aid of one sensor being determined independently of the occupancy probabilities that are ascertained with the aid of measurement values from other sensors and said former occupancy probabilities being used to update the obstacle probabilities of the environment map, the loss of important information is possible, particularly in the case of sensors with a low transverse resolution such as ultrasonic sensors and overlapping fields of view. On account of the low transverse resolution, occupancies (high occupancy probabilities) are ascertained in the transverse direction or azimuth direction for more portions than actually correspond to the extent of the obstacle in the transverse direction. Expressed differently, “elongated” obstacles and other unwanted artifacts arise in the environment map as a result of these effects.
This is disadvantageous for driver assistance functions, particularly for parking and maneuvering assistants, which require not only a distance information item but also an accurate localization of obstacles.
The Applicant's pending application DE 10 2014 208 967 describes a system for capturing surroundings and providing an environment map. Therein, making a distinction between ramps and obstacles, in particular, is highlighted.
The object underlying the invention is that of reducing the aforementioned disadvantages.
This and other objects are achieved by a method and an electronic computing device in accordance with embodiments of the invention.
A first aspect of the invention relates to a method for providing an environment map for a vehicle, wherein the environment map comprises cells which are each assigned to portions of the surroundings of the vehicle and which each have allocated an obstacle probability, the latter representing the probability that the corresponding portion of the surroundings is occupied by an obstacle; wherein the vehicle comprises at least two surroundings sensors, which are each embodied to provide measurement data in relation to the occupancy of a region of the surroundings, referred to as obstacle region, by an obstacle in their respective capture region; wherein the measurement data (only) describe obstacle regions which extend over a plurality of portions of the surroundings; wherein the capture regions of the surroundings sensors overlap at most in part; wherein the method comprises the following steps: receiving the measurement data from the at least two surroundings sensors; wherein the measurement data from a first surroundings sensor have an obstacle region; determining occupancy probabilities for those portions of the surroundings which are covered by the established obstacle region in the measurement data from the first surroundings sensor, depending on the measurement data from at least a further one of the surroundings sensors; wherein an occupancy probability for a portion specifies the probability that the corresponding portion of the surroundings is occupied by an obstacle; updating the obstacle probability of the environment map for at least those portions for which the occupancy probability was determined.
The surroundings sensors are often embodied to recognize the distance to an obstacle, independently of the position of the obstacle in the capture region. Thus, all that is recognized is that, and at what distance, an obstacle is situated in the capture region. Consequently, only this information (and optionally other additional information for processing, but no additional information relating to the position of the obstacle) is consequently comprised in the sensor data from a surroundings sensor.
Thus, what is proposed here is also taking account of the measurement data from a further surroundings sensor when ascertaining the occupancy probabilities on the basis of the measurement data from a surroundings sensor. The occupancy probabilities, by which the environment map is updated, are determined depending on the measurement data from the further sensor. A simple example in this respect is that if the sensor measurement values from the first sensor indicate occupancy but the sensor measurement values from an adjacent sensor indicate no occupancy, the occupancy probability at the edge facing the adjacent sensor is selected to be lower than at the other edge.
By explicitly taking into account dependencies of the sensors among themselves when filling an environment map, it is possible to achieve more accurate and more artifact-free filling of the measurement values into the environment map. This results in fewer interferences and a more accurate localization of obstacles which, for example, significantly improves obstacle-free trajectory planning for automated vehicle guidance on the basis of the environment map and only renders certain driver assistance functions possible, particularly in tight maneuvering scenarios with high demands on the positional accuracy of the obstacles.
When an appropriately configured electronic computing unit is in operation, an environment map substantially is a data structure which comprises cells as subunits that are filled with data relating to the occupancy probability of the corresponding surroundings portion.
Here, occupancy probability, obstacle probability and the term “probability” in general are understood to be measures for the corresponding probabilities and not necessarily the correctly ascertained probability itself.
An obstacle means the presence of a living or non-living object, as a result of which the region of the surroundings occupied by the object is impassible.
If the sensor data from the two surroundings sensors indicate that one sensor has captured an object but the other has not, different occupancy probabilities are determined for at least two different covered portions.
The occupancy probability of the portions of the obstacle occupancy may be determined in accordance with a linear function or any other desired continuous or discontinuous function, with the boundary conditions of the function being predetermined by the sensor data from the considered surroundings sensor and from the adjacent surroundings sensors. Here, provision can be made for only capturing the presence or absence of an obstacle in the respective capture region of the sensor to be of importance for the purposes of determining the boundary conditions. The boundary conditions may set which covered portions are allocated which occupancy probability.
By way of example, the boundary conditions may be determined in such a way that, provided that the considered sensor data indicate an obstacle but the sensor data from the further surroundings sensor do not, the occupancy probability of the portion which is furthest away from the capture region of the further surroundings sensor is set to a predetermined maximum value and the occupancy probability of the portion which is closest to the capture region of the further surroundings sensor is set to a further predetermined minimum value. The occupancy probabilities of the intermediate portions are ascertained in accordance with a linear function.
In so doing, the occupancy probability of the portions that are covered by the obstacle occupancy is determined, up to a constant, in accordance with a linear function or any other desired continuous or discontinuous function, wherein the function is predetermined by the sensor data from the considered surroundings sensor and from the at least one further surroundings sensor. The function may be stored in a predetermined (lookup) table and optionally predetermine occupancy probabilities for all covered portions. In order to predetermine the function, it is possible to take into account whether the sensor data from the surroundings sensors indicate the presence or absence of an obstacle. In this way, it is possible to obtain a similar function, like by the use of boundary conditions, and the aforementioned example can likewise be realized.
The spatial relationship between the capture regions of the first surroundings sensor and of the at least one further surroundings sensor is typically taken into account when determining the occupancy probabilities. If the capture regions of the surroundings sensors are not adjacent or do not overlap (possibly with 0.3 m, 0.5 m or more clear space between the capture regions), the influence of the sensor data from the further surroundings sensor on the occupancy probabilities of the covered portions may be smaller than if the capture regions of the surroundings sensors adjoin one another or do overlap.
In one implementation, the vehicle comprises at least three surroundings sensors, the capture regions of which are next to one another and in each case adjacent to one another and said capture regions overlap at most in part in each case; wherein the method comprises the following steps: receiving the measurement data from the at least three surroundings sensors; wherein the measurement data from the central surroundings sensor have an obstacle region; determining the occupancy probability for those portions of the surroundings which are covered by the established obstacle region in the measurement data from the central surroundings sensor, depending on the measurement data from the two adjacent surroundings sensors. Here, the occupancy probability can be determined depending on whether the measurement data from only one adjacent surroundings sensor or from both adjacent surroundings sensors have an obstacle region.
Hence, in this case, the determination of the occupancy probabilities of the covered portions is dependent on two adjacent sensors. Provision can be made for the occupancy probability of the covered central sections (which at least do not adjoin both adjacent capture regions or have a minimum distance therefrom) to be determined by capturing the obstacle by the central sensor. The occupancy probabilities of the edge portions (not the central portions) can then be determined by the recognized presence or absence of an obstacle in the adjacent capture regions. By way of example, the function for the occupancy probability may be selected depending on the recognized presence or absence of an obstacle. In one embodiment, this may mean that the highest occupancy probability of the covered portions is determined for the occupancy probability of one or more covered portions that do not lie on the edge of the obstacle region if the sensor data from both adjacent surroundings sensors do not have an obstacle region in each case.
In a typical implementation, the obstacle probabilities previously stored in the environment map are complemented by the occupancy probabilities when updating the obstacle probability, in particular its obstacle probability and occupancy probability that are stored for a portion are combined by calculation. The combination by calculation may comprise the summation of the logarithm of the occupancy probability and/or of the logarithm of the obstacle probability, sometimes referred to as “LogOdds”. Hence, the obstacle probability is a filtering of the occupancy probabilities over time, which facilitates the correction of measurement errors. Conversely, the aforementioned methods may also be carried out in such a way that the obstacle probability is set to the occupancy probability. Thus, no filtering is carried out in this case.
Another aspect of the invention relates to an electronic computing device for vehicles, wherein the electronic computing device is configured to carry out one of the methods explained above. The electronic computing device may be a microcontroller, a typical desktop computer, an application-specific circuit or a general computer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
The same reference signs relate to corresponding elements over all figures.